PK Thunder is a PSI attack, introduced in Mother. It is a electricity-based attack that summons bolts of lightning to strike random targets, with more being called down at higher stages. PK Thunder can be reflected by the Franklin Badge in EarthBound and Mother 3.

The probability of Thunder hitting an enemy is calculated as Number of foes/4, and the probability will not decrease if some enemies are defeated before the attack is finished. There is also no elemental resistance for thunder, meaning the damage will never decrease.

PK Thunder is Ness's Special Up move, available in all Super Smash Bros. games. He can redirect it at himself to fire himself at enemies, which does much damage. In Super Smash Bros. Brawl, PK Thunder is once again Ness' Special Up move, but is also now Lucas'. Lucas' is different in the fact that it can move through enemies, while Ness' can't.